How do i merge materials on a pre-textured model without breaking texture mapping
The coordinates you are using before uv unwrapping are called "generated" coordinates, and they aren't actually destroyed by unwrapping, just swapped out. If you look at the node setup you're using to make the procedural texture you started with, you'll notice the textures have inputs for the coordinate mapping. It's possible to manually set them back to generated coordinates without discarding your uv map, allowing you to bake the textures as originally designed.